This invention relates to a cooling scheme for use in an airfoil, such as a turbine blade, wherein a leading edge is supplemented by an additional cooling microcircuit at an area of high stress.
Turbine blades are utilized in gas turbine engines. As known, a turbine blade typically includes a platform, with an airfoil shape extending above the platform. The airfoil is curved, extending from a leading edge to a trailing edge, and between a pressure wall and a suction wall.
Cooling circuits are formed within the airfoil body to circulate cooling fluid, which is typically air. A number of cooling channels extend through the cross-section of the airfoil, and from the platform outwardly toward a tip. Air passes through these channels, and cools the airfoil body, which can become quite hot during operation of the gas turbine engine.
One specialized type of cooling channel is a film cooling channel. A film cooling channel has a number of small holes that direct cooling air outwardly onto an outer surface of the airfoil, with this cooling air then being impinged off of the outer surface to cool the outer surface. One such cooling channel having film cooling holes is positioned near the leading edge of the airfoil. A main cooling channel spaced inwardly from the leading edge typically feeds this leading edge film cooling channel. The leading edge film cooling channel is provided with a number of holes that direct cooling air outwardly onto the outer surface of the airfoil, to provide film cooling on this outer surface.
One area of main design concentration in modern airfoils is the use of varying coatings to provide a number of distinct characteristics to the airfoil. One such coating is a thermal barrier coating that may be placed onto the airfoil to provide some resistance to the airfoil becoming heated to extreme temperatures. Experimental tests of airfoils coated with at least one thermal barrier coating have shown that an area spaced toward the suction wall from the impingement holes of the leading edge film cooling channel has had some erosion in the coating. That is, while the film cooling holes do an adequate job of protecting the coating adjacent the leading edge, an area spaced from the leading edge has had some loss of the coating indicating a need for additional cooling.
Recently, the assignee of the present invention has developed cooling circuits that are embedded into the wall of an airfoil, which have been called microcircuits. These microcircuits are disclosed in a co-pending U.S. patent application Ser. No. 10/637,352, entitled “Microcircuit Airfoil Main Body,” and which was filed on Aug. 8, 2003. These microcircuits have never been disclosed for use at the above area adjacent the leading edge film cooling channel and spaced toward the suction wall.